This invention is in the field of mechanical devices, and relates to filters for reducing pollution from conventional wood-burning fireplaces.
A number of communities have adopted ordinances which are intended to limit the amount of smoke or other pollutants emitted by wood-burning fireplaces. Such ordinances are especially common in ski resort areas and other communities in mountainous areas which have abundant supplies of wood nearby, and in which deliveries of natural gas or fuel oil would be especially expensive, and in various regions where large populations, automobiles, and other factors combine to pose chronic air pollution problems.
However, since it is difficult to limit the amount of smoke emitted by a residential fireplace once it has been built, most such ordinances take the form of zoning-type controls that limit the number of fireplaces which can be built in new developments, and do not make any effort to reduce the amount of smoke emitted by existing fireplaces.
For a number of reasons, a better approach would be to reduce the amount of smoke, dust, and other pollutants emitted by the fireplaces, during use.
Various types of filters have been proposed for the flue channels (this term includes brick chimneys, metallic exhaust pipes, or other fireplace exhaust outlets) of certain types of fireplace assemblies. However, to the best of the Applicants knowledge after a diligent search of the prior art, the only such filters that have been proposed to date are designed as components of large, complex assemblies which comprise complete fireplaces. Examples include the filter assemblies shown in the fireplaces described in U.S. Pat. Nos. 4,279,239 (Blum 1981) and 4,557,687 (Schirneker 1985). Both of these proposed types of filters are contained within large hood-type assemblies that appear to extend from the top of a fireplace opening, all the way up to roughly the height of a ceiling; therefore, these filters cannot be retrofitted into existing fireplaces. In addition, it appears that none of those proposed systems have actually been manufactured and are available for purchase by the public.
Various filters and catalytic converters are used with enclosed wood-burning stoves, and factory smokestacks; examples are described in U.S. Pat. Nos. 4,286,528 (Willard 1981), 4,470,834 (Fasanaro et al, 1984), and 3,706,182 (Sargent 1972). However, as used herein, the term "fireplace" does not include wood-burning stoves which provide a complete enclosure for burning wood, or to incinerators, factory smokestacks, or other such burning chambers. Instead, as used herein, the term "fireplace" is limited to conventional open-hearth fireplaces that are enclosed in front only by mesh-type screens or glass doors, as commonly used in single-family residences, primarily for burning wood (although other fuels such as petroleum-based starter logs, rolled-up newspapers, etc. are often used), and which radiate heat into a room directly from flames that are visible from outside the fireplace.
Although it might appear to be obvious to provide smoke-and-dust filters in the flues of conventional fireplaces, not a single such unit is commercially available, and discussions with several fireplace manufacturers' representatives have indicated several reasons why such units are not being manufactured and sold.
The most important factor involves a fear that if a filter element becomes clogged or otherwise blocked, even if only partially blocked, then air flow out the flue channel will be impeded, and the smoke and hot exhaust gases will exit the front opening and go directly into the room, causing major annoyance and a possible fire hazard. This fear is greatly aggravated by the fact that the hot gases that rise from burning wood contain unburned organic molecules that can condense on any surface that is cooler than the hot exhaust gas, thereby forming creosote, a sticky residue that both (1) greatly increases the danger of clogging a fireplace filter, and (2) poses a fire hazard in its own right, since creosote if flammable if heated sufficiently. Furthermore, if a fireplace filter does become clogged, and smoke begins pouring out of the front opening of the fireplace into the room, the intense heat generated by the fire would make it extremely difficult to reach and manipulate the filter, to replace or remove the filter element.
Another relevant factor concerns air flow and heat conduction in fireplaces. Glass fireplace doors are designed so that they will not be air-tight; they are designed to allow a certain amount of air to pass through the cracks between the doors, to help keep the glass in the doors from becoming overheated. If a filter were to impede the flow of hot exhaust gases out of the flue channel, these glass doors might be jeopardized and might be heated to the point of breaking or warping.
The subject invention discloses a device and method for resolving and overcoming those concerns, and provides a fireplace filter that can operate in a safe and effective manner. It is particularly suited for use in ski resort towns and other areas that restrict or prohibit the installation of new fireplaces.
Accordingly, one object of this invention is to provide a filter-and-fan assembly which can be installed into new fireplaces or retrofitted into existing fireplaces, for filtering dust and smoke (and possibly other agents, such as creosote-generating organic compounds) out of the hot exhaust gases that are created when wood is burned in fireplaces, without creating a major risk of clogging that would create a smoke or fire hazard.
Another object of this invention is to provide a convenient, practical, and relatively inexpensive means for reducing the amount of smoke that is emitted by residential fireplaces in communities that have high numbers of such fireplaces.
These and other objects of the invention will become clear through the following description and drawings.